feat(diagram-engine): open shape vocabulary — catalog + pass-through, structured style merge

The expressiveness gap traced to vocabulary: draw.io has hundreds of shapes,
the declarative layer allowed six. Opening it, with the failure modes from
design review handled:

- shapes.ts: a ~20-entry curated catalog (full style fragment incl. the
  matching perimeter — required or edges connect to the bounding box; a
  text-scale factor verified in the real editor — the same sentence overflows
  a 1.0x rhombus and fits a 1.5x one; labelOutside+glyph for umlActor-style
  figures). Any other token passes through verbatim: draw.io degrades unknown
  shapes to rectangles safely (verified). Injection-capable tokens (;/=) are
  rejected outright.
- Pass-through emits a WARNING with a nearest-catalog hint (bounded edit
  distance), so a typo'd 'cyclinder' is a one-turn fix instead of a silently
  rectangular node forever. set_shape/set_role/set_group operations make the
  fix possible without remove+re-add (which would drop links).
- mergeStyle(): style fragments merge per-key (later wins, bare shape classes
  displace each other) instead of string concatenation. This is what makes
  shape and theme composable by rule — shape owns geometry keys, theme owns
  colour/type keys, and an overlap resolves by order instead of emitting
  contradictory duplicates.
- dai_shape marker carries the declared token through the round trip:
  appearance-based reverse mapping cannot distinguish aliases (diamond vs
  decision) or a rotated queue from a cylinder.
- dai_auto marker separates engine-measured size from user-fixed size: parsed
  boxes no longer freeze the first layout's numbers, so changing a label
  re-measures. Pinned nodes keep everything, as before.
- draw_graph's closed shape enum opened to match (first instance of the
  schema-drift problem the review predicted).

14 new tests: merge ownership, injection rejection, near-match hints,
alias-preserving round trip, re-measure on label change, mxgraph.* tokens
staying boxes with role/group intact. 556 unit tests green; acceptance
diagram (person/hexagon/cylinder/queue/cloud/decision/callout) verified in
the real editor.

lib/diagram-engine/parse.ts

@@ -25,6 +25,7 @@ import { extractDiagramXML } from "@/lib/utils"
 import {
     type Direction,
     hasMarkers,
+    isAutoSized,
     isLaneChrome,
     isPinned,
     MARKER,
@@ -361,6 +362,12 @@ function zoneOf(style: string): string | undefined {
     return v ? decodeURIComponent(v) : undefined
 }
 
+/** The declared shape token stamped on a cell, if any. */
+function shapeOf(style: string): string | undefined {
+    const v = readMarker(style, MARKER.shape)
+    return v ? decodeURIComponent(v) : undefined
+}
+
 /** The flex fields stamped on a cell, as sparse properties ready to spread. */
 function flexOf(style: string): {
     grow?: number
@@ -1069,19 +1076,29 @@ export function parseDiagram(xml: string, pageIndex = 0): ParseResult {
             const headH = lifeline
                 ? Number(styleValue(c.style, "size") ?? "44")
                 : undefined
+            // An engine-measured box must NOT read its size back as a fixed size:
+            // that would freeze the first layout's measurement, so a later label or
+            // shape change would keep the stale box instead of re-measuring. A pinned
+            // node is the exception — the user froze it, geometry and all.
+            const auto = isAutoSized(c.style) && !pinned
             const node: BoxNode = {
                 kind: "box",
                 id: c.id,
                 label: c.value,
-                w: c.geo ? Math.round(c.geo.w) : undefined,
+                w: auto ? undefined : c.geo ? Math.round(c.geo.w) : undefined,
                 h: lifeline
                     ? Math.round(headH && headH > 0 ? headH : 44)
-                    : c.geo
-                      ? Math.round(c.geo.h)
-                      : undefined,
+                    : auto
+                      ? undefined
+                      : c.geo
+                        ? Math.round(c.geo.h)
+                        : undefined,
                 fill: styleValue(c.style, "fillColor"),
                 stroke: styleValue(c.style, "strokeColor"),
-                shape: boxShape(c.style),
+                // The declared token wins: appearance-based reverse mapping cannot
+                // distinguish aliases (decision vs diamond) or identify a passed-through
+                // token whose style is just `shape=<name>`.
+                shape: shapeOf(c.style) ?? boxShape(c.style),
                 role: roleOf(c.style),
                 group: zoneOf(c.style),
                 ...flexOf(c.style),